Method and apparatus for capacitively testing a semiconductor die

ABSTRACT

An apparatus, process for forming an apparatus, and method for testing a semiconductor die having first and second die terminals. The apparatus includes a substrate having a coefficient of thermal expansion approximately equal to a thermal expansion coefficient of the die. The substrate includes first and second test terminals positioned on a surface of the substrate and positionable proximate to the die. The first test terminal is a conductive portion aligned with and spaced apart from a conductive portion of the first die terminal when the substrate is positioned proximate to the die. The first test terminal is coupleable to a variable power source current to generate a variable signal at the first test terminal and capacitively generate a corresponding signal at the first die terminal. The second test terminal is aligned with the second die terminal when the conductive portion of the first test terminal is aligned with the first die terminal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional Application of pending U.S. patentapplication Ser. No. 09/387,649, filed Sep. 1, 1999, which is aDivisional Application of Ser. No. 08/944,598, filed Oct. 6, 1997.

TECHNICAL FIELD

The present invention is directed toward a method and apparatus forcapacitively applying a test signal to a semiconductor die.

BACKGROUND OF THE INVENTION

Semiconductor dies form the core of semiconductor modules and otherdevices which are used extensively throughout the computer industry,telecommunication industry, and myriad related industries. The dies aretypically tested during the manufacturing process to ensure that thedies conform to operational specifications. The resulting dies are theninstalled in the semiconductor module or device.

Semiconductor dies are typically tested by placing conductive test leadsin contact with respective bond pads of the die, applying a test signalto the bond pads via the test leads, and determining whether the dieresponds with the proper output signals. To ensure proper transmissionof the test signals to the die, the test leads may be placed in physicalcontact with the bond pads of the die using a variety of methods. Onemethod is to solder the leads to the bond pads. Another method is tocouple the leads to terminals and then force the terminals intoengagement with the bond pad, deforming both the terminals and the bondpad. One drawback of the foregoing methods is that they include at leasttemporarily connecting the leads or terminals to the bond pads prior totesting and then disconnecting the leads or terminals subsequent totesting. Connecting and disconnecting the leads is time consuming andmay damage the bond pads, making it difficult to permanently install thedie in a semiconductor module when testing has been completed.

One approach to solving the foregoing problem has been to replace thetest leads with test pads, which are capacitively coupled tocorresponding bond pads of the die. The capacitive coupling is formed bya dielectric layer positioned between an electrically conductive portionof the test pad and the corresponding conductive portion of the bondpad. No direct physical contact is required between the conductiveportions of the test pads and the corresponding bond pads. As a result,the likelihood that the bond pads will become damaged by the test padsis reduced. This method may also be less expensive than conductivetesting methods because capacitively coupling and decoupling the bondpads and test pads may require less time and effort than conductivelyconnecting and disconnecting the bond pads and test leads.

Conventional methods for capacitively testing a semiconductor die sufferfrom several drawbacks. The capacitive test pads of a device used totest the die may be large compared to bond pads and may not be alignedwith the bond pads. As a result, an interlayer must be placed betweenthe bond pads of the die and the capacitive test pads. Contacts on thesurface of the interlayer are aligned with the capacitive test pads ofthe test device and are connected through the interlayer to the bondpads of the die. Forming the interlayer requires an additionalmanufacturing step and it may be necessary to remove the interlayerbefore the die may be permanently installed, requiring yet anothermanufacturing step.

Another drawback with a conventional method and device used tocapacitively test semiconductor dies is that the device has a thermalexpansion coefficient which is different than the thermal expansioncoefficient of the die material. As a result, when the die is tested athigh temperatures, the die and the test device expand at different ratesand capacitive coupling may not be maintained between the die and thetest apparatus.

Yet another draw back with conventional testing devices is that thecapacitive test pads may be flush with the surface of the test device.When the test device is placed adjacent the die for testing, dustparticles or other contaminants may become trapped between the testdevice and the die, damaging the die. Still another drawback ofconventional testing methods is that they may require that a liquid orgel dielectric material be placed on the bond pads of the die prior totesting. The liquid or gel dielectric mateial may be difficult to removeafter testing, contaminating the die and inhibiting good connectionsbetween the bond pads of the die and lead wires which are connected tothe bond pads when the die is permanently installed.

SUMMARY OF THE INVENTION

The present invention is a method and apparatus for capacitively testinga semiconductor die or wafer having first and second die terminals. Inone embodiment, the apparatus comprises a substrate positionableproximate the die and having a coefficient of thermal expansionapproximately equal to a thermal expansion coefficient of the die. Theapparatus further comprises first and second test terminals positionedon a surface of the substrate. The first test terminal has a conductiveportion aligned with and spaced apart from a conductive portion of thefirst die terminal. The first test terminal may accordingly becapacitively coupled to the first test terminal when the substrate ispositioned proximate to the die. The second test terminal is alignedwith the second die terminal when the conductive portion of the firsttest terminal is aligned with the first die terminal.

In one embodiment of the invention, the apparatus further comprises adielectric material positioned intermediate the conductive portion ofthe first test terminal and the conductive portion of the first dieterminal. The dielectric material is attached to the conductive portionof the first test terminal in one embodiment and is attached to thefirst die terminal in another embodiment. In yet another embodiment, thedie is one of a plurality of dies comprising a silicon wafer and thesubstrate is sized and shaped to be positioned adjacent the siliconwafer.

The invention is also directed toward a method for manufacturing anapparatus for capacitively testing a semiconductor die having first andsecond die terminals, each connector having a conductive surface. Themethod comprises forming a first test terminal on a substrate such thatthe first test terminal has a conductive surface aligned with and spacedapart from the conductive surface of the first die terminal. The methodfurther comprises forming a second test terminal on the substrate havinga conductive portion aligned with the second die terminal while thefirst test terminal is aligned with the first die terminal. The methodfurther comprises positioning a dielectric material intermediate atleast the conductive portion of the first test terminal and theconductive surface of the first die terminal when the first testterminal is aligned with the first die terminal.

In one embodiment, a method for manufacturing an apparatus in accordancewith the invention further comprises applying a layer of photoresistmaterial to a surface of the substrate, exposing a first region of thephotoresist material to a selected radiation to form an exposed regionof photoresist material, and shielding a second region of thephotoresist material from exposure to the selected radiation to form ashielded region of photoresist material. The method further comprisesremoving one of the exposed and shielded regions, and removing substratematerial previously covered by the other of the exposed and shieldedregions to form a projection which is aligned with the first dieterminal when the substrate is positioned proximate the die.

In yet another embodiment of a method in accordance with the invention,the first test terminal is formed by applying an insulating layer to asurface of the substrate and forming a first portion of conductivematerial on the insulating layer, the first portion of conductivematerial being aligned with the first die terminal when the substrate ispositioned proximate to the die. The method further comprises forming asecond portion of conductive material on the insulating layer alignedwith the second die terminal when the first portion of conductivematerial is aligned with the first die terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of a test apparatus and die inaccordance with a first embodiment of the invention.

FIG. 2 is an exploded isometric view of a die and a substrate of a testapparatus in accordance with the first embodiment of the invention.

FIG. 3 is an exploded, enlarged cross-sectional view of a portion of thesubstrate and die shown in FIG. 2.

FIGS. 4A-4G are schematic cross-sectional views illustrating a method offorming a test apparatus in accordance with an embodiment of theinvention.

FIG. 5 is an exploded, cross-sectional view of a portion of a testapparatus in accordance with a second embodiment of the invention and adie having a dielectric layer overlaying the bond pads thereof.

FIG. 6 is an exploded isometric view of a substrate of a test apparatusin accordance with a third embodiment of the invention and asemiconductor wafer.

FIG. 7 is an exploded, cross-sectional view of a portion of a testapparatus in accordance with a fourth embodiment of the invention and aflip chip.

FIG. 8 is a top plan view of a portion of a test apparatus and die inaccordance with a fifth embodiment of the invention.

FIG. 9 is an exploded, cross-sectional view of a portion of a testapparatus in accordance with a sixth embodiment of the invention and aflip chip.

FIG. 10A is an exploded, cross-sectional view of a portion of a testapparatus in accordance with a seventh embodiment of the inventionhaving compressible test terminals in noncompressed state.

FIG. 10B is an exploded cross-sectional view of the portion of the testapparatus shown in FIG. 10A having compressible test terminals in acompressed state.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed toward a method and apparatus forcapacitively coupling bond pads or terminals of a semiconductor diedirectly to the corresponding test terminals of a test apparatus. Anaspect of one embodiment of the invention is that the test terminals ofthe apparatus are aligned with the corresponding die terminals of thedie. Accordingly, the die need not be modified in any way to align theterminals thereof with the test terminals of the test apparatus. Anotheraspect of an embodiment of the invention is that a substrate of theapparatus may comprise material having the same coefficient of thermalexpansion as that of the die. Accordingly, when the die is tested withthe test apparatus at elevated temperatures, the die terminals remainaligned with the test terminals. FIGS. 1-10B illustrate variousembodiments of the apparatus and methods in accordance with theinvention, and like reference numbers refer to like parts throughout thevarious figures.

FIG. 1 is a cross-sectional view of a test apparatus 10 in accordancewith an embodiment of the present invention engaging a baresemiconductor die 40. The test apparatus 10 comprises a substrate 20having test terminals 60 projecting upwardly therefrom. The testterminals 60 are coupled to die terminals 70 of the die 40 to transmittest signals to the die and receive response signals from the die. Theresponse signals are compared with desired response signals to determinewhether or not the die conforms with operational specifications.

The test apparatus 10 includes a bridge clamp 50 which urges the die 40toward the substrate 20. The bridge clamp 50 is removably attached tothe substrate 20 by passing mounting tabs 55 of the bridge clamp throughslots 21 of the substrate and engaging the mounting tabs with a lowersurface 26 of the substrate. The bridge clamp 50 includes internal tabs53 which engage a spring 51. The spring 51 is bowed downwardly towardthe substrate 20 and engages a pressure plate 54 which in turn engagesthe die 40. The pressure plate uniformly distributes the force suppliedby the spring 51 over the surface of the die 40. When the bridge clamp50 is attached to the substrate 20, the spring 51 urges the pressureplate 54 and die 40 toward the substrate so that the bond pads 70 of thedie firmly engage the test terminals 60 projecting upwardly from thesubstrate. The bridge clamp 50 further includes flanges 52, preferablyformed by bending edges of the bridge clamp downwardly. The flanges 52substantially prevent the bridge clamp 50 from bowing upwardly under theforce of the spring 51.

FIG. 2 is an exploded isometric view of the die 40 and the substrate 20shown in FIG. 1. The die terminals 70 are positioned on a lower surface46 of the die and may comprise bond pads as shown in FIG. 1, or otherstructures as discussed below with reference to FIG. 7. The dieterminals 70 include constant signal die terminals 72 and variablesignal die terminals 71. Both the constant signal die terminals 72 andvariable signal die terminals 71 comprise conductive materials. Theterms constant signal die terminal and variable signal die terminal areused herein to distinguish die terminals which transmit or receive aconstant signal, such as V_(cc) terminals and certain enable terminals,among others, from die terminals which may transmit or receive avariable signal.

The test terminals 60 of the substrate 20 comprise constant signal testterminals 62 and variable signal test terminals 61. The constant signaltest terminals 62 are aligned with constant signal die terminals 72 ofthe die 40 and the variable signal test terminals 61 are aligned withcorresponding variable signal die terminals 71. Accordingly, theconstant signal test terminals 62 of the test apparatus 10 may becoupled to a source of constant power (not shown) and may engage theconstant signal die terminals 72 to form a conductive electricalconnection therebetween and transmit a constant signal to the constantsignal die terminals. The variable signal test terminals 61 may becoupled to a source of variable power (not shown) and may becapacitively coupled to the variable signal die terminals 71 to transmita variable signal to the variable signal die terminals.

The test terminals 60 are preferably positioned in a recessed well 27 ofthe substrate 20 to provide a proper alignment between the testterminals on the substrate and the die terminals 70 on the die 40. Thesubstrate 20 and/or the die 40 may further include visual alignmentmarkings or indentations to further ensure proper alignment between thetest animals 60 and the die terminals 70.

FIG. 3 is an enlarged cross-sectional view of the substrate 20 and die40. The substrate 20 includes projections 30 which extend upwardlytoward the die 40 and form the cores of the test terminals 60. Theprojections 30 have a pyramidal shape in a preferred embodiment and mayhave other shapes in other embodiments. The projections 30 have acenter-to-center spacing D which is approximately 0.005 inch to 0.006inch, corresponding to the spacing between the die terminals 70 of thedie 40. In other embodiments, the spacing D may be less than or greaterthan 0.005 inch to align the projections 30 with bond pads 70 having acorrespondingly smaller or larger spacing, respectively.

In a preferred embodiment, the substrate 20 and the projections 30comprise silicon and the substrate and projections are formedintegrally, as will be discussed in greater detail below with respect toFIGS. 4A-4G. Silicon is a preferred material for the substrate 20because it has the same coefficient of thermal expansion as the siliconcomprising the die 40. Accordingly, when the die 40 is tested at varyingtemperatures, the die and the substrate 20 expand and contract atsubstantially identical rates so that the die terminals 70 of the dieremain aligned with the test terminals 60 of the substrate.

In other embodiments, the substrate 20 may comprise other materialshaving coefficients of thermal expansion similar to or identical withthe thermal expansion coefficient of silicon. Other materials includeceramics, such as Mullite, which is available from Coors TechnicalCeramics Co., Oak Ridge, Tenn. In still another embodiment, thesubstrate 20 may have a thermal expansion coefficient different thanthat of the die 40. An apparatus 10 in accordance with this embodimentmay still be effective when used to test the die 40 at varyingtemperatures if the die is relatively small, and/or if the die terminals70 are relatively large so that the test terminals 60 maintain alignmentwith the die terminals despite the fact that the die 40 and substrate 20may expand and contract at different rates at the varying temperatures.

In a preferred embodiment, the substrate 20, including the projections30, is covered with an insulating layer 22 comprising an electricallyinsulative material. Conductive layers 23 are selectively positionedover the insulating layer 27 to cover each projection 30. The conductivelayers 23 are separated from each other as shown in FIG. 3 so thatelectrical signals may be separately transmitted to or received fromeach test terminal 60. Bond wires 25, some of which are omitted fromFIG. 3 for purposes of clarity, are accordingly connected to eachconductive layer 23 to transmit test signals to or from thecorresponding test terminals 60.

As shown in FIG. 3, the conductive layers 23 completely cover eachprojection 30, including an upper surface 31 and side surfaces 32thereof. In an alternate embodiment, the conductive layers 23 cover theupper surfaces 31 and only one side surface 32 of each projection 30.Accordingly, electromagnetic coupling or “cross talk” between adjacentconductive layers 23 is reduced, reducing the likelihood that electricalsignals transmitted to one test terminal 60 will affect signalstransmitted to a neighboring test terminal.

The variable signal test terminals 61 each include a dielectric layer 24covering the conductive layers 23 which prevents direct contact betweenthe conductive layer 23 and the corresponding variable signal dieterminals 71 when the die 40 is engaged with the test apparatus 10. Thedielectric layer 24 may comprise any number of dielectric materialswhich include but are not limited to nitrides, barium strontiumtitanate, or oxides, such as tantalum pentoxide. The composition andthickness of the dielectric layer 24 is selected to provide a desiredcapacitance between the variable signal test terminals 61 and thevariable signal die terminals 71. The dielectric 24 defines a contactsurface 65 at an upper end of the variable signal test terminal 61 whichis sized to engage a contact surface 75 of the corresponding variablesignal die terminal 71. Where the die 40 includes a passivation layer44, which may extend partially over the die terminals 70, the contactsurface 65 of each variable signal test terminal 61 is preferably sizedto engage the contact surface 75 of the corresponding variable signaldie terminal 71 without resting on the passivation layer, substantiallyeliminating any gap between the contact surfaces 65 and 75. Accordingly,the dielectric constant between each variable signal test terminal 61and corresponding variable signal die terminal 71 is determined by thecomposition and thickness of the dielectric layer 24 and not by a gapwhich might otherwise be formed between the variable signal testterminal and the variable signal die terminal.

In a preferred embodiment, the contact surface 65 is elevated above thesubstrate 20 by a distance that is greater than the thickness of thepassivation layer 44 to ensure that the contact surface 65 of the testterminal engages the contact surface 75 of the variable signal dieterminal 71. In a further preferred embodiment, the contact surface 65is elevated a sufficient distance above the substrate 20 that smallparticles 90, which may comprise dust or other contaminates and whichmay be present between the test terminals 60, do not engage andpotentially damage the die 40.

As shown in FIG. 3, each constant signal test terminal 62 includes aninsulating layer 22 and conductive layer 23 but does not include adielectric layer. Accordingly, the conductive layers 23 of the constantsignal test terminals 62 firmly engage with the corresponding constantsignal die terminals 72 to provide electrical connections therebetween.To further ensure proper engagement between the constant signal testterminals 62 and the constant signal die terminals 72, the constantsignal test terminals are provided with serrations 63 positioned toengage the constant signal die terminals. The serrations 63 releasablypenetrate the contact surface 75 of the constant signal die terminals 72and are separated by stop surfaces 64 to prevent the serrations frompenetrating too deeply into the constant signal die terminals.

In a preferred embodiment, the stop surfaces 64 are positioned such thatthe serrations 63 penetrate one-half the thickness of the constantsignal die terminals 72. In a further preferred aspect of thisembodiment, the stop surfaces 64 are aligned with the contact surfaces65 of the variable signal test terminals 61. Accordingly, when the stopsurfaces 64 prevent further penetration by the serrations 63 into theconstant signal die terminals 72, the contact surfaces 65 of thevariable signal test terminals 61 engage the contact surfaces 75 of thecorresponding variable signal die terminals 71. By aligning the contactsurfaces 65 with the stop surfaces 64, the die 40 will rest solidly onthe test terminals 60 to more reliably transmit electrical signalsbetween the die and the test apparatus 10.

In operation, the test apparatus 10 is used to test the die 40 byplacing the die in the recessed well 27 of the substrate 20 as shown inFIG. 2. The user than aligns the variable signal test terminals 61 ofthe test apparatus 10 with the corresponding variable signal dieterminals 71 of the die 40, and aligns the constant signal testterminals 62 with the corresponding constant signal die terminals 72 asshown in FIGS. 2 and 3. The die 40 is firmly engaged with the testapparatus 10 by first placing the pressure plate 54 on the die and thenclamping the pressure plate and the die against the substrate 20 byinserting the mounting tabs 55 of the bridge clamp 50 through the slots21 of the substrate, as shown in FIG. 1.

Constant signals are then applied to the bond lines 25 connected to theconstant signal test terminals 62 and variable signals are applied tothe bond lines connected to the variable signal test terminals 61. Whena varying signal is applied to the variable signal test terminals 61,the signal is capacitively coupled to the corresponding variable signaldie terminal 71. The varying current may take the form of a singlepulse, an alternating current signal, or any other variable currentsignal. The response signals received from the die 40 may then be usedto determine whether or not the die complies with operationalspecifications and accordingly qualifies as a good die. It will beunderstood that any one variable signal test terminal 61 may transmit orreceive test signals, depending on the characteristics of the particulardie terminal 71 with which it is engaged, and upon the particular phaseof the test process.

One advantage of the method and apparatus shown in FIGS. 1-3 is that thetest apparatus 10 may be used to test the die 40 capacitively couplingtest terminals 61 of the apparatus to variable signal die terminals 71of the die 40, and by supplying a variable current signal to thecapacitive bond pads to test the performance of the die. Conductiveconnections between the test apparatus 10 and die 40 are used only wherethe die requires a constant signal. Accordingly, the number ofconductive connections between the test apparatus and die, which mayphysically damage the die terminals, is reduced.

A further advantage of the test apparatus and method shown in FIGS. 1-3is that the variable signal test terminals 61 of the test apparatus 10are aligned with the corresponding variable signal die terminals 71 ofthe bare die 40 when the die is engaged with the test apparatus. Thealignment is maintained even where the center-to-center spacing betweenthe die terminals is on the order of 0.005 inch to 0.006 inch, or less.Accordingly, a user need not manipulate the die 40 in any way to alignthe variable signal die terminals 71 of the die with the variable signaltest terminals 61 of the test apparatus 10. Unlike conventional methods,the user need not add to the die 40 a layer which includes intermediateterminals which are electrically connected to the die terminals 70, butspaced to correspond to the locations of the variable signal test padsof a test device. As a result, testing of the bare die 40 isconsiderably simplified.

Yet a further advantage is that the substrate 20 shown in FIGS. 1-3 maycomprise a material having a coefficient of thermal expansion similar toor identical with the thermal expansion coefficient of the die 40.Accordingly, the test apparatus 10 may be used to test the die 40 atvarying temperatures while maintaining alignment between the dieterminals 70 of the die 40 and the test terminals 60 of the testapparatus.

Still a further advantage of an embodiment of a test apparatus 10 isthat the nature of the capacitive coupling between the test apparatus 10and the die 40 may be controlled by controlling the thickness and/orcomposition of the dielectric layer 24. The user accordingly has greatercontrol over the capacitance between the test apparatus 10 and the die40 by manipulating two variables. Furthermore, unlike conventionalmethods, controlling the dielectric constant between the die 40 and thetest apparatus 10 requires only manipulating the test apparatus and notthe die itself. Unlike conventional methods, which may require that adielectric liquid or gel be placed on the variable signal die terminals,the test apparatus 10 requires no contamination of the variable signaldie terminals, which may be difficult to remove after testing has beencompleted.

A method for fabricating an apparatus 10 having variable signal testterminals 61 in accordance with an embodiment of the invention is shownin FIGS. 4A-4G. As shown in FIG. 4A, the method includes providing asubstrate 20 having a substantially flat upper surface 28. In apreferred embodiment, the substrate 20 may comprise silicon, and maycomprise other materials in other embodiments, as discussed below. Theupper surface 28 of the substrate 20 is coated with a layer of positiveor negative photoresist material 82. As shown in FIG. 4B, a mask 80 isthen placed upon the photoresist material 82. The mask 80 may preferablybe an exact or nearly exact mirror image of a mask used to form the dieterminals 70 on the die 40. Accordingly, the test terminals 60 formed bythe mask 80 will have locations corresponding exactly or nearly exactlywith the locations of the die terminals 70 when the die 40 is placedface down on the substrate 20.

Where the photoresist material 82 is a positive photoresist material,the mask 80 have apertures 81 which correspond to the locations of thedie terminals 70 of the die 40. Where the photoresist material 82 is anegative photoresist material, the apertures 81 correspond to theregions between the die terminals 70. For purposes of illustration, thephotoresist material 82 is shown as being positive in FIGS. 4A-4G.

The substrate 20 with photoresist material 82 and mask 80 in place, isexposed to a selected radiation 83 which hardens the photoresistmaterial 82 a located beneath the apertures 81 while leaving thephotoresist material 82 b beneath the mask 80 in a nonhardened state. Itwill be understood that where a negative photoresist material is used,the photo resist material 82 b is hardened while the photoresistmaterial 82 a remains in a non-hardened state. After exposure to theselected radiation 83, the mask 80 is removed and the photoresistmaterial 82 rinsed in a chemical bath, which washes away the unhardenedphotoresist material 82 b while leaving the hardened photoresistmaterial 82 a in place, as shown in FIG. 4C.

The substrate 20, with the hardened photoresist material 82 a in place,is then exposed to an etching solution which anisotropically etches awayportions of the substrate not covered by the photoresist material 82 aand creates the projections 30 as shown in FIG. 4D. The hardenedphotoresist material 82 a is the removed. Alternatively, the substrate20 may be exposed to an oxidizing agent which oxidizes the surface ofthe substrate not covered by the photoresist material 82 a. The oxidizedportion may then be stripped leaving the projections 30 in place.

In an alternate method of manufacture, the projections 30 may be formedby depositing material on the upper surface 28 of the substrate 20. Inone such embodiment, the photoresist layer 82 is eliminated and the mask80 is placed directly on the substrate 20. Material comprising theprojections 30 is then deposited using an overhead ion depositionapparatus or similar device to build the projections up from the uppersurface 28 of the substrate 20. Such an alternate method may be usedwhere the substrate 20 comprises a ceramic or other material which maynot be as conducive as silicon to etching. The resulting projections 30may be planarized using chemical-mechanical planarization to flatten theupper surfaces 31 of the projections 30. The flattened upper surfaces 31accordingly provide the foundation for test terminals 61 having flatcontact surfaces 65 which mate well with the corresponding flat contactsurfaces 75 of the variable signal die terminals 71 (FIGS. 3).

Ridges 33 may be formed on the projects 30 which will form constantsignal test terminals 62. The ridges may be formed using photoresist andetching techniques similar to those discussed above and described ingreater detail in U.S. Pat. No. 5,483,741 to Akram et al. and U.S. Pat.No. 5,326,428 to Farnworth et al., both of which are incorporated hereinby reference.

The insulating layer 22 is formed on the projections 30, as shown inFIG. 4E. In one method of manufacture, in which the substrate 20comprises silicon, the substrate is exposed to an oxidizing atmosphereto form a layer of silicon dioxide (SiO)₂, an electrically insulativecompound. In alternate embodiments, SiO₂ or Si₃N₄ may be deposited onthe surface of the substrate 20 by chemical vapor deposition. In yetanother alternate embodiment, tetraethylorthosilane (TEOS) is injectedat high temperature into a chamber surrounding the substrate 20 to growin insulating layer 22 of SiO₂ on the substrate 20. In still anotheralternate embodiment, the insulating layer 22 is deposited on thesubstrate 20 by chemical vapor deposition or similar depositiontechniques. Such an alternate embodiment may be used where the substrate20 comprises a ceramic material which does not oxidize as readily asdoes silicon.

The conductive layers 23 comprising a conductive material are formedatop the insulating layer 22, as shown in FIG. 4F. In one embodiment, aninitially continuous conductive layer 23 may be deposited on theinsulating layer 22 using chemical vapor deposition. A photoresist andmasking process, similar to that discussed above with reference to FIGS.4A-4D, may then be used to etch away portions of the conductive layer 23located between the projections 30 to form individual conductive pathsto each projection. As discussed previously with reference to FIG. 3,the conductive layers 23 may be etched to cover the entirety of eachprojection 30, or may be etched to cover the upper surface 31 of eachprojection and enough of a side surface 32 to form a conductive path tothe projection.

The conductive layer 23 and insulating layer 22 conform to the ridges 33of the constant signal test terminal 62, forming the serrations 63. Theserrations 63 may be further roughened by using an electroplatingprocess and controlling the composition of the electrolyte solution usedin the process to form a textured or roughened surface which amplifiesthe serrated surface created by the etching process. The formation ofroughened electroplated surfaces is further discussed in U.S. Pat. No.5,487,999 to Farnworth, incorporated herein by reference.

The dielectric layers 24 are formed on the conductive layers 23 of thevariable signal test terminals 61, as shown in FIG 4G. In oneembodiment, an initially continuous dielectric layer 24 is deposited onthe conductive layer 23 by chemical vapor deposition. In anotherembodiment, the initially continuous dielectric layer 24 may bedeposited using an electrophoretic process to form an even layer ofdielectric over the projections 30. An electrophoretic process isdescribed in U.S. Pat. No. 5,607,818 to Akram et al., which isincorporated herein by reference. The electrophoretic process includescharging the conductive layer 23, either positively or negatively, andimparting the opposite charge to the dielectric material. The dielectricmaterial is accordingly attracted to the conductive layer 23 andgradually builds up the dielectric layer 24 thereon. An advantage of theelectrophoretic process is that it results in an even coating ofdielectric material over the conductive layer 23 notwithstanding thenon-uniform topography created by the projections 30. Another advantageis that the electrophoretic process is self-limiting because of theconductive layer 23 becomes coated with dielectric material, it tends tohave less affinity for additional dielectric material. Accordingly, theamount of dielectric material electrophoretically deposited on theconductive layer 23 may be controlled by controlling the charge appliedto the conductive layer. Furthermore, the dielectric layer tends to bethicker at higher temperatures than at lower temperatures. Accordingly,the temperature at which the electrophoretic process is carried out maybe used to further control the dielectric characteristics of thedielectric layer 24.

Once a continuous dielectric layer 24 has been formed, portions of thedielectric layer may then be etched away using a photoresist and maskingprocess similar to the process discussed above with reference to FIG.4A-4D. Dielectric material located between the projections 30 may beremoved as shown in FIG. 4G to isolate the variable signal testterminals 61 from each other. In addition, any dielectric materialcovering the constant signal test terminals 62 may be removed to ensureproper electrical contact between the constant signal test terminals andthe corresponding constant signal die terminals 72.

An advantage of the process discussed above with reference to FIGS.4A-4G is that the process uses a mask layer 80 which is a mirror imageof the mask layer used to create the die terminals 70 on the bare die40. Accordingly, the projections 30 which form the test terminals 60 ofthe test apparatus 10 may be precisely aligned with the correspondingdie terminals 70 of the bare die 40. As a result, the need to form aninterlayer between the die 40 and the test apparatus 10 is eliminated,as discussed above with reference to FIGS. 1-3. A further advantage ofthe process shown in FIGS. 4A-4G is that the dielectric layer 24 isformed on the test apparatus 10, eliminating the need to removably applyliquid or gel dielectric substances to the die 40, as was also discussedabove with reference to FIGS. 1-3.

FIG. 5 is an exploded, cross-sectional view of a test apparatus 10 inaccordance with a second embodiment of the invention, and a die 40having dielectric layers 24 a attached to the variable signal dieterminals 71 thereof. In one embodiment, the dielectric layers 24 a maycomprise oxide coatings which form naturally on the metallic dieterminals 70. In other embodiments, the dielectric layers 24 a maycomprise other organic dielectric materials which may be deliberatelyformed on the variable signal die terminals 71.

In the embodiment shown in FIG. 5, the dielectric layers 24 areeliminated from the variable signal test terminals 61 of the testapparatus 10 because their function is performed by the dielectriclayers 24 a on the variable signal die terminals 71. Accordingly, thecontact surfaces 65 a of the variable signal test terminals 61 comprisea portion of the conductive layer 23 as shown in FIG. 5, rather than aportion of the dielectric layer 24 as shown in FIG. 3.

In one embodiment, the serrations 63 of the constant signal testterminals are capable of penetrating the dielectric layer 24 a formed onthe constant signal die terminal 72. The serrations accordingly form aconductive connection with the constant signal die terminal 72notwithstanding the presence of the dielectric material. In anotherembodiment, the dielectric layers 24 a may be prevented from forming onthe constant signal die terminals 72 so that the constant signal testterminals 62 form solid conductive contacts with the constant signal dieterminals. In still another embodiment, the dielectric layers 24 a maybe removed from the constant signal die terminals 72 by using maskingand etching process, as discussed previously with reference to FIGS.4A-4D.

An advantage of an embodiment of the test apparatus shown in FIG. 5 isthat the test apparatus requires no dielectric layer 24. Accordingly, atleast one process step required to form the test apparatus 10 may beeliminated. Conversely, an advantage of an embodiment of the testapparatus shown in FIGS. 1-3 is that the die 40 need not be manipulatedto either form or remove the dielectric layer.

As discussed above, the dielectric oxide layers may form naturally onthe dies 40. The oxide layers may form after the dies have beenelectrically partitioned from each other on a silicon wafer but remainin a wafer form. To take advantage of the naturally occurring dielectriclayers, a test apparatus 10 in accordance with a third embodiment of theinvention is sized to accommodate and test an entire wafer 100comprising a plurality of partitioned dies 40, as shown in FIG. 6. Thetest apparatus 10 comprises a substrate 20 having slots 21 toaccommodate a bridge clamp. (not shown). The bridge clamp is used toreleasably couple the wafer 100 to the substrate 20, as discussedpreviously with reference to FIG. 1. The substrate 20 comprises testterminals 60, which are aligned with corresponding die terminals 70 atthe wafer 100. Accordingly, variable signal test terminals 61 arealigned with variable signal die terminals 71 and constant signal testterminals 62 are aligned with constant signal die terminals 72, asdiscussed previously with reference to FIGS. 1-3.

An advantage of the test apparatus 10 shown in FIG. 6 is that it permitsa user to engage the test apparatus with an entire wafer 100 of dies 40in one operation. Accordingly, the user need not individually engageeach die 40 with the test apparatus 10 before testing and then removeeach die after testing. A further advantage is that the test apparatus10 shown in FIG. 6 may use the oxide layer naturally forming on the dies40 of the wafer 100 to act as dielectric layers between the dieterminals 70 of the dies and the test terminals 60 of the testapparatus, reducing the number of processing steps required to producethe test apparatus 10, as discussed above with reference to FIG. 5.

FIG. 7 is an exploded, cross-sectional view of a test apparatus 10 inaccordance with a fourth embodiment of the invention positioned adjacenta flip chip 40 a in FIG. 7. As shown in FIG. 7, the die terminals 70 aof the flip chip 40 a include a variable signal die terminals 71 a andconstant signal die terminals 72 a. The die terminals 72 a may comprisesolder balls formed from lead or a similar soft, conductive material.Each die terminal 70 a has an end surface 76 spaced apart from the lowersurface 46 of the flip chip 40 a and a side surfaces 77 intermediate theend surface and the lower surface of the flip chip. The die terminals 70a may have an oxide coating 78 which covers the bond pads and deformswhen the flip chip 40 a is engaged with the substrate 20. The oxidecoating 78 generally deforms sufficiently to create a conductiveelectrical connection between the die terminals 70 a and the testterminals 60 against which they press. Accordingly, the oxide coating 78is not relied upon to form a dielectric layer between the variablesignal die terminals 71 a and the variable signal test terminals 61 aswas discussed above with reference to FIG. 5. Instead, the dielectriclayer 24, positioned on the variable signal test terminals 61, providesthe capacitive coupling between the test apparatus 10 and the flip chip40 a, substantially as discussed above with reference to FIGS. 1-3.Furthermore, because the oxide layer 78 deforms when the flip chip 40 ais pressed into engagement with the substrate 20, the contact betweenthe constant signal test terminal 62 and the constant signal dieterminal 72 a is sufficient to create a constant signal connectiontherebetween, as discussed above. The need for serrations on theconductive test terminals 62 is accordingly eliminated.

FIG. 8 is a top plan view of a portion of a test apparatus 10 inaccordance with a fifth embodiment of the invention shown engaging aportion of a flip chip 40 a. The test apparatus 10 shown in FIG. 8 issimilar to the apparatus shown in FIG. 7 except that the contactsurfaces 65 b of the test terminals 60 are positioned parallel to theside surfaces 32 rather than the upper surfaces 31 of the projections 30(FIG. 7). Accordingly, the side surfaces 77 of the die terminals 70slide along the contact surfaces 65 b of the test terminals 60 as theflip chip 40 a is pressed into engagement with the substrate 20.

As shown in FIG. 8, pairs of test terminals 60 having diagonally opposedcontact surfaces 65 b may be oriented in an alternating pattern tosubstantially prevent lateral motion of the flip chip 40 a relative tothe substrate 20 once the die terminals 70 a have been engaged with thetest terminals 60. The test terminals 60 accordingly aid the user inorienting the flip chip 40 a relative to the substrate 20 and maintainthe orientation until the die is deliberately disengaged from the testapparatus 10.

FIG. 9 is an exploded, cross-sectional view of a portion of a testapparatus 10 in accordance with a sixth embodiment of the invention. Thetest apparatus 10 comprises a substrate 20 without large projections 30.Instead, the insulating layer 22, conductive layers 23, and dielectriclayers 24 are consecutively formed directly on the upper surface 28 ofthe substrate to form variable signal test terminals 61 a and constantsignal test terminals 62 a. In the embodiment shown in FIG. 9, theprojections 30 are not necessary to provide an offset between thesubstrate 20 and the flip chip 40 a. Instead, the solder balls of theflip chip 40 a provide a sufficient offset between the substrate 20 andthe flip chip 40 a to prevent dust particles or other contaminants 90from becoming clamped therebetween. An advantage of an embodiment of thetest apparatus 10 shown in FIG. 9 is that the process steps required toform raised projections may be eliminated, simplifying the manufactureof the test apparatus 10.

FIG. 10A is an exploded, cross-sectional view of a portion of a testapparatus 10 in accordance with a seventh embodiment of the inventionhaving compressible test terminals 60 b. The substrate 20 includes aninsulating layer 22 and conductive layers 23 formed directly thereon.The projections 30 a are formed atop the conductive layers 23 in asubsequent step. The projections 30 a comprise a conductive materialwhich may be sputtered or spun on the conductive layers 23 or may bedeposited on the conductive layers using chemical vapor deposition. Theresulting continuous layer may then be etched using the photoresist andmasking techniques discussed previously with reference to FIGS. 4A-4G toform individual projections 30 a.

In one embodiment, the projection 30 a may be formed from anincompressible conduction material. In another embodiment, theprojections 30 a may be formed from a compressible, conductive materialsuch as a z-axis elastomer. Such elastomers are available from Zymet ofEast Hannover, N.J. The elastomer contains conductive particles 34 whichare dispersed therethrough and are shown schematically in FIG. 10A. Whenthe elastomer is compressed in a direction normal to the upper surface28 of the substrate 20, the particles 34 come into contact with eachother and create a conductive path through the elastomer.

Dielectric layers 24 are then applied atop the conductive layers 23 ofthe variable signal test terminals 61 b. The dielectric layers 24preferably comprise a flexible material, such as a polyamide, which willflex as the projections 30 a compress. The polyamide may be appliedusing a spray process or an electrophoretic process, such as wasdiscussed previously with reference to FIG. 4G. As discussed previouslywith reference to FIG. 3, no dielectric layer is applied to the constantsignal test terminals 62 b, so as to provide conductive connectionsbetween the constant signal test terminals and the constant signal dieterminals 72.

In operation, the die 40 is compressed against the substrate 20 so as tocompress the projections 30 a, creating conductive paths from theconductive layers 23 through the projections, as shown in FIGS. 10b. Thevariable signal test terminals 61 form capacitive connections with thevariable signal die terminals 71 and the constant signal terminals formconductive connections with the constant signal die terminals 72, asdiscussed previously with respect to FIGS. 1-3.

An advantage of the test apparatus shown in FIGS. 10A and 10B is thatthe compressible test terminals 60 b flex in a vertical direction whenthe die 40 is engaged with the substrate 20. The test terminals 60 baccordingly maintain an electrical coupling with the die terminals 70 ofthe die 40 even if the lower surface 26 of the die is not parallel withthe upper surface 28 of the substrate. A further advantage is that thecompressible constant signal test terminals 62 b are biased toward thecorresponding constant signal die terminals 72, increasing thelikelihood of a good conductive connection therebetween and eliminatingthe need for serrations on the constant signal test terminals.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

What is claimed is:
 1. A method for testing a semiconductor die havingfirst and second die terminals, the method comprising: providing a testapparatus having first and second test terminals and a layer ofdielectric material other than a native oxide material attached to thefirst test terminal, the first and second test terminals being alignablewith the first and second die terminals, respectively, the layer ofdielectric material having a thickness that permits the first testterminal to be capacitively coupled with the first die terminal so thata test signal is transmitted therebetween; aligning the first testterminal with the first die terminal and the second test terminal withthe second die terminal; capacitively coupling the test signal from thefirst test terminal to the first die terminal; and varying a temperatureof the die and test apparatus to vary a size of the die and a size ofthe test apparatus.
 2. The method of claim 1 wherein providing a testapparatus having first and second test terminals and a layer ofdielectric material other than a native oxide material attached to thefirst test terminal comprises providing a test apparatus having firstand second test terminals and a layer of a nitride material attached tothe first test terminal.
 3. The method of claim 1 wherein providing atest apparatus having first and second test terminals and a layer ofdielectric material other than a native oxide material attached to thefirst test terminal comprises providing a test apparatus having firstand second test terminals and a layer of oxide material attached to thefirst test terminal.
 4. The method of claim 1, further comprisingmaintaining alignment between the first test terminal and the first dieterminal and between the second test terminal and the second dieterminal as the temperature of the die and test apparatus are varied. 5.The method of claim 1 wherein providing a test apparatus comprisesproviding a test apparatus having a substrate comprising a siliconmaterial.
 6. The method of claim 1 wherein providing a test apparatuscomprises providing a test apparatus having a substrate comprising aceramic material.
 7. The method of claim 1 wherein capacitively couplingthe test signal from the first test terminal to the first die terminalcomprises capacitively coupling a variable signal from the first testterminal to the first die terminal.
 8. A method of testing asemiconductor die having first and second die terminals, the methodcomprising: providing a test apparatus having first and second testterminals and a layer of dielectric material other than a native oxidematerial proximate the first test terminal, the first and second testterminals being alignable with the first and second die terminals,respectively, the layer of dielectric material being intermediate thefirst test terminal and the first die terminal and having a thicknessthat permits the first test terminal to be capacitively coupled with thefirst die terminal so that a test signal is transmitted therebetween;aligning the first test terminal with the first die terminal and thesecond test terminal with the second die terminal; and capacitivelycoupling the test signal from the first test terminal to the first dieterminal.
 9. The method of claim 8 wherein providing a test apparatushaving first and second test terminals and a layer of dielectricmaterial other than a native oxide material proximate the first testterminal comprises providing a test apparatus having first and secondtest terminals and a layer of a nitride material proximate the firsttest terminal.
 10. The method of claim 8 wherein providing a testapparatus having first and second test terminals and a layer ofdielectric material other than a native oxide material proximate thefirst test terminal comprises providing a test apparatus having firstand second test terminals and a layer of an oxide material proximate thefirst test terminal.
 11. The method of claim 8, further comprisingreceiving an output signal from the die.
 12. The method of claim 8wherein providing a test apparatus comprises providing a test apparatushaving a substrate comprising a silicon material.
 13. The method ofclaim 8 wherein providing a test apparatus comprises providing a testapparatus having a substrate comprising a ceramic material.
 14. Themethod of claim 8 wherein capacitively coupling the test signal from thefirst test terminal to the first die terminal comprises capacitivelycoupling a variable signal from the first test terminal to the first dieterminal.
 15. The method of claim 8, further comprising varying atemperature of the die and test apparatus.
 16. The method of claim 8,further comprising coupling the second test terminal to a source ofconstant power.
 17. The method of claim 8, further comprisingcapacitively coupling the second test terminal with the second dieterminal.
 18. The method of claim 8, further comprising releasablybiasing the die into engagement with the test apparatus.
 19. A method oftesting a semiconductor die having first and second die terminals, themethod comprising: providing a test apparatus having a substrate, firstand second conductive projections extending away from the substrate andalignable with the first and second die terminals, respectively, thetest apparatus including a portion of a dielectric material other than anative oxide material attached to the first projection and positionedintermediate the first projection and the first die terminal when thefirst projection is aligned with the first die terminal, the portion ofdielectric material having a thickness that permits the first projectionto be capacitively coupled with the first die terminal so that a testsignal is transmitted therebetween; aligning the first conductiveprojection with the first die terminal and the second conductiveprojection with the second die terminal; and capacitively coupling thetest signal from the first conductive projection to the first dieterminal.
 20. The method of claim 19 wherein providing a test apparatusincluding a portion of a dielectric material other than a native oxidematerial comprises providing a test apparatus including a portion of anitride material.
 21. The method of claim 19 wherein providing a testapparatus including a portion of a dielectric material other than anative oxide material comprises providing a test apparatus including aportion of an oxide material.
 22. The method of claim 19 whereinproviding a test apparatus having a substrate comprises providing a testapparatus having a silicon substrate.
 23. The method of claim 19 whereinproviding a test apparatus having a substrate comprises providing a testapparatus having a ceramic substrate.
 24. The method of claim 19 whereincapacitively coupling the test signal from the first conductiveprojection to the first die terminal comprises capacitively coupling avariable signal from the first conductive projection to the first dieterminal.